1. Field of the Invention
This invention concerns the preparation of a lithium complex soap grease having a high dropping point.
2. Description of Related Art
Various batch processes have been suggested for preparing lithium complex soap thickened greases. For example, U.S. Pat. No. 2,898,296 discloses a process in which the dicarboxylic acid is converted to an ester prior to reaction with lithium hydroxide. As another example, U.S. Pat. No. 2,940,930 discloses a process wherein a polyhydric alcohol or glycol is added to the monobasic or dibasic acid mixture before lithium hydroxide is added. In U.S. Pat. No. 3,681,242, the monocarboxylic acid and the dicarboxylic acid components are neutralized together, but the process requires two distinct heating steps following neutralization. In yet another example, U.S. Pat. No. 3,791,973 discloses a process which requires separate neutralization and heating steps for the monocarboxylic fatty acid and the dicarboxylic acid components. However, the separate neutralization steps result in extended production times. More recently, U.S. Pat. Nos. 4,435,299 and 4,582,619 disclose a single stage batch process that requires direct neutralization of the acids and one heating stage thereafter, but with carefully controlled alkali addition in which the temperature must be maintained below the boiling point of water during preparation of the grease. However, the slow rate of alkali addition also results in extended production times.
Continuous processes for manufacturing lithium complex soap thickened greases are also known. For Example, U.S. Pat. No. 4,444,669 discloses a continuous process for preparing a high dropping point lithium complex soap grease in which the oil, acids, and base are reacted at the same time and the temperature is maintained above the boiling point of water during neutralization. However, continuous processes have the disadvantage of less operational flexibility than batch processes. For this reason, almost all existing grease plants and equipment are for batch processes.
Accordingly, there is a need for a method of preparing a high dropping point lithium complex soap grease that utilizes existing grease plant equipment, but reduces the production time associated with batch processes.